Method of forming mica-insulated spark plugs



Aug-16 1932- A f H. R/luanzzzllm/ u v 1,872,497

METHOD 0F FORMING MIG INSULATED SPARK PLUGS Filed Dec. '7, i928 Patented Aug. 16, 1932 [UNITED STATES PATENTv OFFICE micron nABEzzANA, OF FLINT, M'IOHIGAN, Ass'IGNOa 'ro A c srAnx PLUG COMPANY, or FLINT, MICHIGAN. A CORPORATION or MICHIGAN METHOD F FORMING MICA-INSULATED ySPARK PLUGS Application led December 7, 1928. Serial No. 324,513.

As indicated by the above title, the present invention, in its specific aspect, relates t0 spark plugs; and it has particular reference to a method or process of producinga spark plug of that type in which mica, or the like, is used as an insulatin material. It relates also to a novel and dura le spark plug formedk by said method or process; and it is a partielllar object of this invention, usingiannular laminae of mica or other suitable material, assumed to be in the form of washer-s, to produce a conduction unit comprising a compact, durable, and solid body disposed about a ccntral conductive element,such as a tensionable rod or wire, threaded at one end, and serving as an electrode permanently sealed against leakage.

The present invention involves, in apreferred embodimentmeans and methods, of securingannular laminae, or the like, under a predetermined axial compressiom-weakened portions of exteriormetallic elements, comparable with those described in my Patent No. 1,609,735, granted December 7, 1926, but differing therefrom in form, relationships and function, being so collapsed as,V to buckle or bulge inwardly, after the compression of the mica, or its equivalent, by a pressure applied axially of the mentioned tensionable element; and, in case electrical or other heating is employed in softening and/or inwardly expanding the mentioned weakened portion this invention may utilize further lateral and longitudinal pressures which result from the contraction of said weakened portions upon the associated metallic or other tensionable members during a subsequent cooling to nor- `mal temperature,the f result being an insulated unit whosev compactness and impermeability to gases are exceedingly permanent and reliable.

Notwithstanding its easy cleavage in parallel lanes and because of its great resistance to ame and to sudden temperature changes, as well as normal acid-resisting qualities which render it substantially impervious to engine gases, being a poor conductor of both heat and electricty, mica is a very desirable material for use as insulation in the spark 5 plugs of internal combustion engines,-espe formed from a number of initially separate vgroove so positioned as locally Ito reduce the cially in high speed and high compression engines; and it is accordinglya general object of this invention to provide both improved spark'plugs andan improved tech-v nique in the utilization of mica in-insulation.

Heretofore, mica insulators have sometimes been made by threading a quantity of mica Washers upon a centra-l wire member, a metallic shell being externally shrunk thereon and insulated by a mica sleeve surrounding the central wire,the washers beingcompressed by suitable tools and held by a nut or end piece screw-threaded to the central wire; but-that arrangement has been found` subject to looseness and consequent leakage, by reason of the .unavoidable expansion and contraction. of the external metallic y parts while in use upon an engine; and it has provided nopermanently ras-tight joints to seal the insulator from lea age,-dependingentirely upon the mentioned screw-threaded endpiece or nut; and, althougha mica as- .sembly so built up about a central wire has sometimes been ostensibly sealed by cementing (as well as by the mentioned shrinking of a metallic shell thereon) such assemblies have beenv observed to deteriorate in time by reason of the engine action and the mentioned expansion and contraction of the metallic part-s; and it is accordingly an object of this invention, recognizing that mica possesses great flexibility, elasticity, and toughness, and is thereby particularly adapted to be compressed to a compact and solid mass discs, to overcome the difficult-ies heretofore encountered,said diiculties being herein attributed tothe lack of proper means for holding the mica discs or washers in a compact body and with proper sealing joints surrounding a central tensionable element such as the mentioned Wire or a 'suitable rod or tube as required in spark plug insulation. Other objects of this invention, including a novel method of permanently securing a 05 stop or clamping elementfupon a tensionable rod, with or without interposition of a tubular element, said stop orclamping element being initially provided with an annular washers vbeing cross-sectional area thereof and provide a weakened section which is adapted to bulge inward under a suitable application of'pressure and withV or without a concurrent low of electricity through said reduced section, to soften the same, may best be appreciated from the following description of illustrative embodiments of this invention, taken in connection with the appended claims and the accompanying drawing. I

Fig. 1 is a general view, with parts broken away to a median plane, showing a so-calle two-part spark plug produced in accordance with thel principles of this invention.

Fig. 2 is a longitudinal sectional view, takensubstantially as indicated by the line 2-2 of Fig. 1, but including only an inner electrode organization,`to which the present inventionA is more particularly directed.

Figs. 3-6 are respectively diagrammatic sectional vvievvstaken similarly to Fig. 2, but

illustrating successive steps (and some optional features) in the productionof a spark, plug such as that shown in preceding figures. Fig. 3 shows relationships before compression.

Fig. 7 is a detail view, corresponding to an upper portion of Fig. 6,-to` aid in the visualization of uniting e fects which are hereinafter described.

Fig. 8 is a bottom plan view of' the spark plug shown in Fig. 1, better to disclose one advantageous form of outer electrode or sparking element. Y

Fig. 9 is -a sectional view, corresponding to the lower portion of Fig. 1 but showing an alternative type of outer electrode or sparking element.

Referring to details of that embodiment of the present invention chosen for purposes ofillustration, it will be understood that, in the preparing and dressing of mica for use in the ractice ofthis invention, so-called books o mica are split in a known manner into sheets of 'suitable thickness, so-calle'd punched from the mentioned sheets; but not all steps of the selected embodiment of the present invention are deemed to be in need of illustration or ei:e planation.

In Fig. 3, a central wire or rod'15 is shown as having been provided, atits lower end, with `an enlarge of a head 16,-'-suitable to serve asa substantially flat and upwardly facing shoulder for a mica assembly; and a first insulating element or mica washerlayer 17 is assumed to have been placedIupon'the central rod ory wire 15. An insulating sleeve 18, which may have been. formed of a suitable composition or from rolled mica, may have been rolled upon a suitable arbor (not shown) orl it may now be disposedupon the wire or rod 15, a second insulating unit or assembly 19, shown as a layerof mica washers having a slightly upon a large scale,

xtinuedor subsequent endwise pressure,

vThis operation,

stop element in the -form thereof from a circular threaded portion 2lb,

vis placed over the tube 20,-said shell being preferably slightly longer than said tube and so reduced in thickness by kerf 21 as to provide, inwardly thereof, a weakened section 210, having a relatively high resistance to electrical current by reasonsof its limited.

cross-sectional area. Mica-protective tube 20 m'ay be formed of copper.

The assembled or partially assembled unit may then be placed Ain a suitable press or socalled welding machine, as represented by lsuitable formed and oppositely disposed die or pressure elements 22, 23 adapted to apply to the mentioned parts a suitable pressure in y the general direction of the axis of wire or rod 15; an electrical or other means (as symbolized lby a plus sign and a minus sign in Figs. 3, 4 and 6) may be'used previously or simultaneously to heat the shell 21 or the weakened section 210 to a red or other suitable temperature of slight plasticity,- adapting the same to so collapse,'under con that the wall of the shell buckles or bulges inwardly in the mentioned region,-somewhat as indicated at 24, Fig. 4.

The described method will be seen to provide an annular rib or bead, inwardly projecting about the sleeve 18 and/or the tube 20; and the foregoing operations are presumably carried to the point ofl forcing and deforming the said tube inwardly, atthe same time fusing and practically forming a weld between the shell 21 and the tube 20.

diminishing kerf 21", may incidentally provide a similar bulge 25 upon the tube 20,--which will press and extend into the mica sleeve 18, forcin the latter 've tightly to embrace the rod or wire 15 an rmanently exerting a circumferentially b eanng pressure which is adapted Submintially to close any porous voids in the sleeve 18 or between the other contacting surfaces,- the shell or bushing 21 being optionally shortened during these operations to permit die 22, or its equivalent, directly to apply some longitudinal ressure to tube 20, as an aid to the mentioned inward buckling thereof.

It will be seen that the comp mica washers, or their equivalent, are retained under a desired high pressure because the 'y collapsing of the weakened section is accom'- plished in such manne to avoid any inequality'of' compressiomhis eect, in turn being due to the factthat only\the constric 'element 25.

portion of the shell 21 is highly heated, the pressure to which the mica washers are subject being controlled according to the pressure and temperature at which the weakened portion will so collapse as substantially to diminish the electrical resistance thereof and/or by a longitudinal shortening of the shell 21,-and thecontraction of metallic parts in cooling to normal room temperature being, in any case, effective not only to maintain but to increase the pressure under which the mica, or its equivalent, is held.

As diagrammatically suggested inFigs. 3 and 4, one of a pair of contact elements 24', 24 may be so positioned that a predetermineddownward advance of the die element 22, or its equivalent, to produce an inward buckling of the weakened Section 210, automatically effects a discontinuance of current therethrough; and it will be understood that the mentioned method and/or the mentioned use of the brass tube 20, or its equivalent, prevents any such bulging of the shell 21 as might cause the same to project and cut through the mica sleeve 18, or its equivalent. The clamping pressure exerted by the described steps, including the shrinking of the resultant annular rib of the shell 21 which rib commonly unites, as by welding, to the tube 20) has been found to be such that a hammer will not drive off or loosen the lgrip of the mentioned outer parts, hereinyafter referred to as mica assembly A, upon the rod or wire 15.

The wire or rod 15 is shown as provided additionally with an upper or outer mica assembly B, comprising al third insulating element 22', adapted to fit over the sleeve 18, and a fourth insulating element 22, the latter having a central aperture so restricted as to fit directly and snugly upon the wire or rod 15, and the last-mentioned element being shown as retained by a final stop or clamping The general construction of the clamping element 25 and the method of positioning and securing the same may be substantially the same as above described in connection with the shell 21.

That is to say, the clamping or nut element 25 is shown as provided with a comparatively deep kerf 25', with the result that com-.

paratively wide and rugged portions 25a, 25?) thereof are connected by a weakened portion 250 having a reduced cross-section and corn` paratively high electrical resistance, so that a suitable application of pressure, as by means of a so-called die element 26, may be relied upon to so deform the clamping element 25, `producing an inward bulge in the region of the weakened section 25o (through which an electrical current may be passedI in the indicated manner) as permanently to secure said clamping element (assumed initially to have a smooth bore) upon a threaded semblies being either successively or simultaneo usly secured in the general manner described; but it is ordinarily deemed preferable separately to execute the described operation-employing the die 26 in' connection with a cooperating die (shown as adapted to engage the non-circular portion 21a of the shell 21) and adapting the die 26, flat or of a configuration indicated at 265, to impart some inward pressure incidentally to the vapplication of longitudinal pressure thereby. The result may be a partial fusing or welding union between the rod or wire 15 and the clamping nut 25, in substantially the general manner suggested in Fig. 7, upon thermoplastic deformation.`

An inner electrode spindle, formed in the general manner described, may obviously be' incorporated in a so-called one-piece spark plug or in a so-called two-piece spark pluga form of the latter being shown in Fig. 1 as comprising a conductive body which is internally threaded at 28 for engagement1 9,-the latter being presumably4 the more du.-

rable, and the former better adapted to certain specific conditions of use, as will be understood by workers in this field.'

Under certain conditions, pressure without electric heat may be employed in the above process; and it will be obvious that, according to circumstances, either or both of a pair of stop or binding elements com, parable with 16 and 21 or y21 and 25 v,or 16 and 25 (at least one of said stop elements being initially annular and movable), may be secured to some central tensionable element such as the wire or rod 15, after an appropriate application of pressure therethrough to intermediate laminae or other'assemblies or units; that when separate yassemblies ofy laminae, or like insulating partsare to be used in contact with an intermediateshell 21, or its equivalentl (as in the case of assemblies A and B, shown as formed from outer or small-opening sections 17 and 22 having associated therewith large-opening sections 19 and 22') they may be externally provided with a desired taper, or with any special con'- figuration and/or polish either before or "C" after (but preferably after) being permanently bound in the described general manner; that any of the mentioned parts (as end pieces 25) may be cut and/or polished incidentally to machining and like operations; that anyv interior use of cement or softenable insulating materials (somewhat as suggested at 32 and 32 in Figs. 3 and 4, and as suggested at 33 Vand 33 in Figs. 5 and 6) should be regarded as ordinarly unnecessary; and that the tube 20, when used, may .-well have a length intermediate between the initial length and the final length of the shell 21; but, if formed of mica or a similar material, the sleeve 18, when used, should be of such length as to leave a clearance space 34 at one end thereof. A lustrous an exceedingly durable product results,-not subject to leakage, chipping or warping.

Referring further to features which are entirely optional, one or both of a co-operating pair of die or pressure elements (as, the

element 23) may be advanced or supported by means including some pressure-responsive element,-as symbolized in Fig. 4 by a spring 35; and the wiring details schematically shown in Fig. 4 and 6 will respectively suggest that the breaking of a contact, as at 24, Fig. 6, may resulteither from a predetermined shortening of an applied clamping element or from the attainment of a predetermined maximum pressure thereon, and that, in either case, a discontinuance of current through any pressure-applying means may be* incidentally effected; but it will be understood that the arrangement shown in Fig. 6 differs from that shown in Fi 4 in requiring or permitting some con uction through the rod 15; that alternative means may be employed, in preference to the spring 35 (yielding under a predetermined pressure--say one ton per square inch) to support a part such as inner insulation assembly A during a compression thereof and yet to obviate risk of v the employment of a higher pressure (sa two tons per square inch) to effect a slight y subsequent and vinward deformation of an annular retaining element; that, to assure an enhanced and permanent compression by' contraction upon cooling, electrical heating, when employed, should vbe discontinued before the dies are permitted to separate; that the principles of this invention are by no means limited to the production of the disclosed double-insulated inner electrode assembly'or unit; that either the conductive stem or rod 15 or a collapsible element disposed thereon may be provided with threads or other projections adapted to be partially stripped to assure good contact and reliable retention; that, although threads thereon adapt the outer end of the rod 15 to carry an additional nut or nuts, to engage conductors in a known manner, and the described prodamage thereto during and the nut 25, or

not recommended; and that a permanently high longitudinal tension and a high radial compression of the central wire or rod 15 or Vits equivalent, may

by a proper execution of the described compression and heating steps in some electrical welding machine of a known type. Although the foregoing mentof the present invention, various alternatives being incidently suggested, it should be understood not only that various features thereof may be independently employed but that numerous modifications, additional to those mentioned herein, might easily be devised,-without involving the slightest departure from the spirit and scope of this invention.

I claim:

l. A method of placing a part under comression upon a rod-like element 4and securing a pressure-maintaining annular element thereon which comprises: so weakening said annular element by a peripheral groove as to adapt a region thereof to inward distortion under longitudinal compression; and applying thereto such longitudinal pressure as first to compress said part to the desired degree and then inwardly to distort said region 'into a nonslipping engagement with said rodlike element.

2. A method of placing a part under compression upony a rod-like element and securing a pressure-maintaining annular element thereon which comprises: so weakening -said annular element by a/peripheral groove as to adapt a region thereof to inward-distortion under longitudinal compression; and applying thereto such longitudinal pressure as first to compresssaid part to the desired degree and then inwardly to distort said reon into a nonslipping engagement with said rod-like element, suicient heat bein applied to one of said elements, during sai application of pressure thereto, to soften said region.

3. A method of placing a part under compression upon a rod-like element and securing a pressure-maintaining annular element conveniently be assuredl description has included complete details of but one embodithereon which comprises: so weakening said as first to compress said part to the desired degree and then inwardly to distort said region into a nonslipping engagement with said rod-like element, suiiicient heat being applied, by means of an electrical current, to.

tudinal pressure as first to compress said part to the desired degree and then inwardly to distort said region into a nonslipping engagement with said rod-like element, one of said elements being threaded.

5. A method of securing an insulating sleeve between a rod-like element and a tube which comprises: surrounding said tube by an annular element having a pre-weakened region thereof adapted as to permit of its distortion under longitudinal pressure; and.

applying thereto such longitudinal pressure as to produce, by an inward distortion in said region, an annular constriction in said tube.

6. A method of securing an insulating sleeve between a rod-like element and a tube which comprises: surrounding said tube by an annular element having a pre-weakened region thereof adapted as to permit of its distortion under longitudinal pressure; and simultaneously applying thereto sufficient heat to soften the same and such longitudinal pressure as to produce, by an inwardv distortion in said region, an annular construction in said tube.

7. A method of securing an insulating sleeve between a rod-like element and a tube which comprises: surrounding said tube by an annular element having a region thereof so weakened as to permit of itsdistortion under longitudinal pressure; and applying thereto such longitudinal pressure as to produce, by an inward distortion in said region, an annular constriction in said tube, said region being a region having a relatively restricted cross section and high resistance, and said heating being effected by passing electricity therethrough.

8. A method suitable for use in providing a central tensionable element carrying a stop element with an assembly of mica insulation which comprises: so disposing the ,assembly upon said tensionable element as t0 be reta-ined by said stop element; disposing a metallic shel-l element provided with a weakened region upon said assembly; comressinfr said assembl between said sto ele- P e ment and said shell element; and so inwardly Adistorting said weakened region as to prevent subsequent slippage of parts relatively to said conductive element.

9. A method'as defined in claim 8 in whicli,

an insulating sleeve and a tube being disposed betweensaid tensionable element and said shell, the mentioned distortion is so executed as to produce a constriction in said tube, compressing said sleeve between said tube and said tensionable element.

10. In the production of substantially gastight spark plugs, a method characterized by the fact that a metallic element which has nonvitreous insulation disposed therein is givensuch an internal diameter while hot as radially to compress said insulation upon cooling. Y

1l. A method as defined -in claim 10 in which aprotecting tube is interposed between said metallic element and said insulation in advance of said deformation.

12. A spark plug spindle comprising: an4

inner electrode, mica sleeve insulation and mica washer insulation thereon; and retaining elements therefor including a metallic intermediate element and a metallic terminal element, one of said metallic elements having been heated under a mica-compacting pressure and thermoplastically collapsed axially thereof for a retaining effect.

13. For use in an article' of the general character set forth: a thermoplastically collapsible retaining elementl comprising a body provided with an annular external channel, defining a zone which is adapted initially to transmit a compressive thrust and later to undergo a collapse,-to exert sealing and retaining eii'ects both when hot and on cooling.

14. A double insulated inner electrode spark plug unit comprising: a-tensionable electrode; and an inner insulation assembly and an outer insulation assembly secured thereon under compression by, means .comprising a collapsed retaining element insu'- `lated from, but `secured against longitudinal element in the form of a shell comprising a .threaded portion and a noncircular portion separated by a weakened region which is adapted to be inwardly distorted under pressure.

1 7. The method of assembling spark plugs which includes the disposition about a compres'sible insulator sleeved on an electrode of an annular retainer element having a prepared collapsible region, and the application of longitudinal pressure on said retainer element to shorten the length thereof by the collapse of said region so as to exert a radially inward compression of the insulator sleeve.

' 18. The method of securing to a rod-like part an apertured member having a reduced neck portion, which includes inserting the rod-like part through the aperture of the member, then heating said neck portion to soften the same, and placin axial pressure on the member to collapse t e softened neck and contract the aperture. y .Y f 19. The method of assembling spark plugs or the like, which includes insertin an electrode in an insulator sleeve, surroun ing the sleeve with an annular retainer having a. reduced neck, heating said neck to soften the same and placing. endwise pressure on the retainer to axially collapse the softened neck and thereby orm an interior lbul e that compacts the s eeve about the electrode.

20. The method of assemblingv spark plugs, which includes placing insulation on an electrode,"and applying pressure on a retainer element to first compact longitudinally a portion of the insulation and then deform the element to compact radially another por-l tion of the insulation and to bind the retainer element in position on the electrode. l

21. The method of assembling spark plugs, which includes interposing a body of compressible insulation between an abutment on anelectrodelelement and an annular element sleeved on the electrode element, compressing said insulator body between the abutment andY annular element, heating a p0rtion of the annular element to soften the same, and 'applyin to collapse te heated portion thereof, into a locking relation with the electrode element. 22. The method of assembling spark plugs, which includes interposing a compressible insulator body between a stop carried by the central electrode and a retainer element fitted to the electrode, compressing said insulator body and then molecularly uniting the* retainer element and electrode to permanently maintain the insulator body under compression.

23. The method of assembling spark plugs, which includes interposing a compressible insulator body between a stop carried by the central electrode and a retainer element .fitted to the electrode, applying endwise pressure to said retainer to axially compact said insulator body, and applying heat to a portlon of the retainer to soften the same for collapse under endwise applied pressure so as to'tix itto the electrode and thus maintain the insulator body under permanent compression.

In testimony whereof I affix my signature.

Lavalin? axiallpressure on said element 

